This is also useless:
Can you tell me when k will EVER be equal to k+1? Answer: never. So the condition is always true. That wouldn't cause an error though - it's just bad programming.
Also, id, when you do get around to defining it. Must be a 2-D matrix.
And you might want to preallocate y in advance, though it's not necessary.
And finally, there are no comments. All professional programmers put comments in their code to help them understand later what they did, or to help others understand what they did. I don't really know what you're trying to do. Maybe there is a function or one vectorized line of code to do it, but since there are no comments, I don't know.